Under "LAYERS" in the sidebar, you should see a layer called "obstructions" (you might have to scroll down). Click on that layer and your TILES palette should switch to a different set of black-and-white tiles. Just paint those down like normal tiles. In the game, you won't see the white or black, but any white pixel in the obstruction layer will stop the character from moving.

Ben McGraw's lovingly crafted this website from scratch for years.
It's a lot prettier this go around because of Jon Wofford.
Verge-rpg.com is a member of the lunarnet irc network, and would like to take this opportunity to remind you that regardless how babies taste, it is wrong to eat them.